European Journal of Pain, 2025 · DOI: https://doi.org/10.1002/ejp.4775 · Published: January 1, 2025
This study investigates how the brain's natural pain control systems interact with the spinal cord's pain processing mechanisms. Researchers explored whether activating descending pain modulation (top-down control) could block the amplification of pain signals in the spinal cord. The study used both human participants and rats to compare pain responses. In humans, they measured pain perception using pinprick tests and cuff pressure. In rats, they recorded nerve activity in the spinal cord during similar pain stimulation. The findings suggest that under the tested conditions, the spinal cord's pain amplification mechanisms were stronger than the brain's descending inhibitory controls. Additionally, pupil dilation was found to be an unreliable measure of pain modulation activity.
Dampening facilitatory mechanisms rather than augmenting top-down inhibitory processes may be a more effective pain-relief strategy for individuals exhibiting inefficient conditioned pain modulation and/or high temporal summation of pain.
Pupil dilation may not be a reliable indicator of endogenous pain modulatory processes, particularly at lower stimulus intensities.
The concordance between human psychophysical and rat spinal neuronal responses supports the translational validity of these models for studying pain mechanisms.